/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.flink.streaming.api.functions.timestamps;

import org.apache.flink.annotation.PublicEvolving;
import org.apache.flink.streaming.api.functions.AssignerWithPeriodicWatermarks;
import org.apache.flink.streaming.api.watermark.Watermark;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import static java.util.Objects.requireNonNull;

/**
 * A timestamp assigner and watermark generator for streams where timestamps are monotonously
 * ascending. In this case, the local watermarks for the streams are easy to generate, because they
 * strictly follow the timestamps.
 *
 * @param <T> The type of the elements that this function can extract timestamps from
 */
@Deprecated
@PublicEvolving
public abstract class AscendingTimestampExtractor<T> implements AssignerWithPeriodicWatermarks<T> {

    private static final long serialVersionUID = 1L;

    /** The current timestamp. */
    private long currentTimestamp = Long.MIN_VALUE;

    /** Handler that is called when timestamp monotony is violated. */
    private MonotonyViolationHandler violationHandler = new LoggingHandler();

    /**
     * Extracts the timestamp from the given element. The timestamp must be monotonically
     * increasing.
     *
     * @param element The element that the timestamp is extracted from.
     * @return The new timestamp.
     */
    public abstract long extractAscendingTimestamp(T element);

    /**
     * Sets the handler for violations to the ascending timestamp order.
     *
     * @param handler The violation handler to use.
     * @return This extractor.
     */
    public AscendingTimestampExtractor<T> withViolationHandler(MonotonyViolationHandler handler) {
        this.violationHandler = requireNonNull(handler);
        return this;
    }

    // ------------------------------------------------------------------------

    @Override
    public final long extractTimestamp(T element, long elementPrevTimestamp) {
        final long newTimestamp = extractAscendingTimestamp(element);
        if (newTimestamp >= this.currentTimestamp) {
            this.currentTimestamp = newTimestamp;
            return newTimestamp;
        } else {
            violationHandler.handleViolation(newTimestamp, this.currentTimestamp);
            return newTimestamp;
        }
    }

    @Override
    public final Watermark getCurrentWatermark() {
        return new Watermark(
                currentTimestamp == Long.MIN_VALUE ? Long.MIN_VALUE : currentTimestamp - 1);
    }

    // ------------------------------------------------------------------------
    //  Handling violations of monotonous timestamps
    // ------------------------------------------------------------------------

    /**
     * Interface for handlers that handle violations of the monotonous ascending timestamps
     * property.
     */
    public interface MonotonyViolationHandler extends java.io.Serializable {

        /**
         * Called when the property of monotonously ascending timestamps is violated, i.e., when
         * {@code elementTimestamp < lastTimestamp}.
         *
         * @param elementTimestamp The timestamp of the current element.
         * @param lastTimestamp The last timestamp.
         */
        void handleViolation(long elementTimestamp, long lastTimestamp);
    }

    /** Handler that does nothing when timestamp monotony is violated. */
    public static final class IgnoringHandler implements MonotonyViolationHandler {
        private static final long serialVersionUID = 1L;

        @Override
        public void handleViolation(long elementTimestamp, long lastTimestamp) {}
    }

    /** Handler that fails the program when timestamp monotony is violated. */
    public static final class FailingHandler implements MonotonyViolationHandler {
        private static final long serialVersionUID = 1L;

        @Override
        public void handleViolation(long elementTimestamp, long lastTimestamp) {
            throw new RuntimeException(
                    "Ascending timestamps condition violated. Element timestamp "
                            + elementTimestamp
                            + " is smaller than last timestamp "
                            + lastTimestamp);
        }
    }

    /** Handler that only logs violations of timestamp monotony, on WARN log level. */
    public static final class LoggingHandler implements MonotonyViolationHandler {
        private static final long serialVersionUID = 1L;

        private static final Logger LOG =
                LoggerFactory.getLogger(AscendingTimestampExtractor.class);

        @Override
        public void handleViolation(long elementTimestamp, long lastTimestamp) {
            LOG.warn("Timestamp monotony violated: {} < {}", elementTimestamp, lastTimestamp);
        }
    }
}
